|  | 4.3 | Layer 1 Design
| 4.3.3 | HCC, VCC, MDF, IDF, and POP

When hosts in larger networks are outside the 100-meter limitation for Category 5 UTP, it is not unusual to have more than one wiring closet. By creating multiple wiring closets, multiple catchment areas are created. The secondary wiring closets are referred to as IDFs. TIA/EIA 568-A Standards specify that IDFs should be connected to the MDF by using vertical cabling, also called backbone cabling. As shown in figure , A vertical cross-connect (VCC) is used to interconnect the various IDFs to the central MDF. Because the vertical cable lengths typically are longer than the 100-meter limit for Category 5 UTP cable, fiber-optic cabling normally is used, as shown in figure .
| Threaded Case Study
Washington Project: Connection Speeds

In the Washington School District network, the vertical cabling should carry all data traffic between the IDFs and MDFs. Therefore, the speed of this connection should be designed to be the fast link in the network. All traffic across the district network backbone will traverse this link, so this link should be at least 100 Mbps.